Remove support for Javy.JSON

[jeffcharles]

Description of the change

Removes Javy.JSON.fromStdin and Javy.JSON.toStdout APIs and associated configuration options.

Why am I making this change?

These were non-standard APIs and can now by implemented by Javy plugins instead of inside Javy itself.

Checklist

• I've updated the relevant CHANGELOG files if necessary. Changes to javy-cli and javy-plugin do not require updating CHANGELOG files.
• I've updated the relevant crate versions if necessary. Versioning policy for library crates
• I've updated documentation including crate documentation if necessary.